Gas-liquid heat exchangers have numerous applications. For example, in vehicles, gas-liquid heat exchangers can be used to cool compressed charge air in turbocharged internal combustion engines or in fuel cell engines. Gas-liquid heat exchangers can also be used to cool hot engine exhaust gases.
Various constructions of gas-liquid heat exchangers are known. For example, it is known to construct gas-liquid heat exchangers comprised of two or more concentric tubes, with the annular spaces between adjacent tubes serving as fluid flow passages. Corrugated fins are typically provided in the flow passages to enhance heat transfer and, in some cases, to join together the tube layers.
Coaxial or concentric tube gas-liquid heat exchangers have the advantage that they are relatively compact and inexpensive, making them suitable for use in vehicles. However, durability of concentric tube heat exchangers can be a concern. For example, thermal stresses resulting from differential thermal expansion of the various tube layers can lead to premature failure of concentric tube heat exchangers. The differential thermal expansion is due to the fact that one or more of the tubes will be in contact with the relatively hot gases, whereas at least one of the tubes will be in contact with the relatively cool liquid. The problem of differential thermal expansion has been partly addressed in the prior art by leaving the fins unbonded to one or both of the tubes with which they are in contact, for example as disclosed in U.S. Pat. No. 3,474,513 to Allingham. This permits relative longitudinal expansion of the tube layers while avoiding excessive thermal stresses. However, leaving the fins unbonded can reduce heat transfer from the fins to the tubes, and may permit longitudinal slippage or displacement of the tubes relative to one another.
Therefore, there remains a need for coaxial or concentric tube heat exchangers which are effective and efficient in terms of operation, use of space and durability.